Wastewater treatment is a process which makes polluted water suitable for domestic or industrial use. The polluted water may contain undesirable and toxic contaminants, in particular metal contaminants. Further, the water can be polluted by human waste, industry waste, agricultural waste or any other source. Such polluted water and also any other polluted liquids are hazardous to environment if they are released into rivers, streams or sewers directly. Therefore, treatment of such polluted water and any other polluted liquids is of utmost importance in view of the damage to the environment as well as stringent environmental regulations.
Numerous techniques for metal removal and recovery processes are known including precipitation, absorption and biosorption, electro-winning and electrocoagulation, cementation, membrane separation (reverse osmosis and electro dialysis), solvent extraction and ion exchange. However, these techniques have limited applicability.
There have been a number of solutions provided for improved and efficient metal removal from contaminated aqueous solutions and few of them have been discussed below:
U.S. Pat. No. 4,992,179A describes a process for treating an aqueous solution containing heavy metal cations to remove the cations by sorption and recover the metal cations using microbial cells having metal uptake properties. A biomass reaction product is produced by treating the cells with a caustic solution, whereby the biomass reaction product after drying is having substantially enhanced uptake of the metal cations from the aqueous solution.
Another method of removing metal ions is disclosed in U.S. Pat. No. 6,379,551B1. The disclosed method removes metal ions from an organic fluid containing metal ions using an ion exchange membrane. The ion exchange membrane is having a porous polymeric support grafted with an organic moiety to which at least one ion exchange group is covalently bonded. Further, a filtration apparatus is disclosed for removing ions from the fluid using the ion exchange membrane.
Yet another method for removing heavy metals from contaminated water is disclosed in U.S. Pat. No. 8,419,946B2. An adsorbent composition for removing heavy metals from contaminated water is also disclosed. In the method, a stream of water having a concentration of one or more heavy metals is passed through adsorbent comprising granules. The granules are made of a mixture of from about 1 wt % to about 15 wt % clay and a thermoplastic polymer matrix.
The aforesaid documents and similar disclosures which talk about varied methods for removal of metals from the contaminated aqueous solution comprises number of shortcomings and drawbacks such as limited applicability, energy requirement, low absorption capacity and requirement for precise control. Further, synthetic ion-exchange resins used in the conventional methods require reverse flushing of packed column to regenerate the resin, whereby a metal contaminated flushing fluid is produced which makes disposal difficult. Also, ion exchange media selected according to the ion-exchange resins used, may have limited flow rates and channeling problems. In addition, the existing methods are expensive, complex and time consuming.
Accordingly, there remains a need in the prior art to have an improved method for removal of metals from aqueous solutions which overcomes the aforesaid problems and shortcomings.
However, there remains a need in the art for a method for removal of metals from aqueous solutions. The proposed method utilizes natural biomaterials and/or microorganisms for the removal of metals from the aqueous solutions. Further, the method is easy, cost effective and environmental friendly.